Burst-and-coast swimmers optimize gait by adapting unique intrinsic cycle

Abstract

This paper addresses the physical mechanism of intermittent swimming by considering the burst-and-coast regime of fish swimming at different speeds. The burst-and-coast regime consists of a cycle with two successive phases, i.e., a phase of active undulation powered by the fish muscles followed by a passive gliding phase. Observations of real fish whose swimming gait is forced in a water flume from low to high speed regimes are performed, using a full description of the fish kinematics and mechanics. We first show that fish modulate a unique intrinsic cycle to sustain the demanded speed by modifying the bursting to coasting ratio while maintaining the duration of the cycle nearly constant. Secondly, we show using numerical simulations that the chosen kinematics by correspond to optimized gaits for swimming speeds larger than 1 body length per second.

Intermittent propulsion in largemouth bass, Micropterus salmoides , increases power production at low swimming speeds

“…Our results suggest a mechanistic explanation based in muscle physiology for predictions in the literature that intermittent swimming minimizes cost of transport (e.g. [18]). Empirical measurements of power output from isolated muscle bundles allow us to make predictions for future metabolic studies of muscle function and swimming behaviours in fishes.…”

“…Intermittent swimming is a more recently described swimming behaviour in fishes proposed to reduce energy costs at steady, sustainable swimming speeds [16][17][18]. In field studies and laboratory observations, swimming fish will routinely employ a sustainable, aerobic muscle-powered intermittent swimming behaviour in which 2-3 tailbeats are alternated with approximately 1 s glide periods [1,[19][20][21][22].…”

“…Importantly, this has been generally observed when fish are swimming volitionally in static water as opposed to induced flows in a laboratory swim tunnel. Modelling of intermittent swimming behaviour using the red or aerobic myotome in this alternating manner suggests a reduction in energetic costs [16][17][18]. Gliding in a straight body position reduces drag compared to an undulating body, leading to the prediction of lower muscle activity and lower energetic costs when gliding and undulation are alternated [20].…”

Learning swimming escape patterns for larval fish under energy constraints

“…As can be seen in Figure 5 (b), the peak speed is attained earlier for higher energies so the duty cycle decreases as the energy budget increases. In contrast, experimental data on the duty cycle of fish swimming at cruising speeds indicates that fish increase their duty cycle when higher speeds are required [55]. This suggests, that for escapes where high acceleration is required in order to increase escape distance in a fixed amount of time, the Duty Cycle of burst-coast strategies should be made as small as possible.…”

Body Caudal Undulation Measured by Soft Sensors and Emulated by Soft Artificial Muscles

“…2A and B ). Fish modulate an inherent cycle to preserve the necessary speed by varying the ratio of bursting to coasting while keeping the cycle length approximately constant ( Li et al. 2021 ).…”